PROJECT SUMMARY (ABSTRACT) Among adults living with HIV in the United States, between 20% and 40% are affected by depression. Depression negatively affects retention in care, antiretroviral (ART) adherence, sustained viral suppression, and survival. The majority of HIV patients with a depressive disorder also have one or more co-existing anxiety, post-traumatic stress, alcohol, or substance use disorders. These co-occurring disorders both complicate depression treatment and, if left untreated, represent additional important barriers to HIV treatment. To comprehensively address the psychiatric barriers to HIV care engagement, depression treatment interventions must be flexible enough to also address these psychiatric comorbidities. Standard pharmacological and psychotherapeutic interventions for depression, anxiety, PTSD, and substance use are effective among people with HIV.36-40 However, training interventionists in multiple protocols for multiple diagnoses is labor-intensive and leads to disconnects in treatment. As an alternative, recent advances in transdiagnostic interventions offer a promising unified framework for comprehensively addressing psychiatric comorbidity while enhancing HIV care engagement. Transdiagnostic treatment approaches capitalize on the common elements in interventions for depression, anxiety, PTSD, and substance use to offer tailored, integrated treatment to individuals presenting with any combination of the disorders. One such proven transdiagnostic intervention, the Common Elements Treatment Approach, or CETA, is based on the elements of cognitive behavioral therapy common to treatments for depression, anxiety, PTSD, and substance use disorders. CETA was developed to be delivered in low-income countries by supervised lay health workers, and has demonstrated efficacy in improving depression, anxiety, and PTSD among survivors of trauma in Thailand and Iraq; it has further been adopted for community health roll-out by the state of Washington. CETA has not previously been adapted for the particular needs of people living with HIV or specifically to address HIV care engagement. However, CETA is ideally positioned for this purpose because of its unified approach to treating psychiatric comorbidity, the ease of integrating additional cognitive behavioral content relating to HIV care engagement, and its design for delivery by non-specialists. We propose to adapt CETA for the particular needs of adults receiving HIV care in the US and pilot-test the adapted intervention to assess acceptability, feasibility, fidelity, and preliminary indications of impact. We hypothesize that the adapted CETA intervention will be acceptable to patients and providers, will prove feasible to integrate in a busy HIV primary care setting, will be delivered with fidelity, and will demonstrate preliminary indications of impact in improving HIV and mental health outcomes. This proposal will generate critical evidence to guide the design of a full-scale RCT to test the effectiveness of the adapted CETA protocol in improving HIV treatment and mental health outcomes for this vulnerable population.